Controlling the acid level (or pH) during and after fermentation is another
means to influence the flavor and character of your home brewed mead. Must
should be slightly acidic since spring water should have a pH of 7 and honey has
a pH around 3.9. Yeast prefer an acidic environment, but many other organisms
don’t. This helps the yeast get a jump on other organisms that could ruin your
mead or impart off flavors. Simple and inexpensive kits are available at most
home brew shops that will contain everything you need, and teach you how to test
for the pH level.

Tartaric, Malic, and Citric are the most common acids used to influence the
flavor and pH of mead. Any combination of these acids can be used, and most acid
blends sold contain a mixture of all three. Tartaric is the dominant acid in
grapes, Malic is the dominant acid in apples, peaches, pears, watermelon, and
bananas, and Citric is the dominant acid in lemons, limes, and many citrus
fruits. Natural fruit juices also be used to influence acid levels. Each acid
has a distinct flavor, experiment with them to learn which you like best.

There is some debate as to whether acid should be adjusted before fermentation
or after. Must will become more acidic as the yeast metabolizes sugars. If the
initial pH is too low, the yeast may stop metabolizing sugars, or impart off
flavors as the pH continues to drop. On the other hand, if the starting pH is
too high, the yeast may face increased competition from bacteria which can spoil
the mead or impart off flavors.

Adding acid after fermentation is most often done to influence flavor, not the
pH level. Since fermentation is complete, you are able to add acids or fruit
juices to taste. Acids added after fermentation can help to offset the cloying
sweetness of honey in a very sweet mead.

Our Recommendation:
You should monitor the pH of the must before fermentation, but we only recommend
adding acid if the pH is higher than 6.0. This is only slightly acidic which
will benefit the yeast, but should not result in a very low pH after
fermentation. Additional acids or fruit juices can be blended in to taste after
fermentation. If adding fruit juice, make sure the yeast is inactive so that
fermentation does not start up again.

There are pros and cons to both approaches, you should try both and see which
method you prefer.